The present invention relates, in general, to the technical field of the check valves or the flow control valves, intended to be inserted in circuits through which fluids flow, in particular gaseous fluids. More particularly, this invention relates to the structure of a check valve of the type having a flexible membrane, and yet more particularly to the “seat” portion of such a valve, that is to say the portion on which the membrane is urged in the closing position of the valve, preventing the passage and more precisely the backflow of the fluid. The check valve with flexible membrane, subject-matter of the invention, finds applications in particular in the automotive field, inside various systems which utilize depression for their operation.
In automotive vehicles, there are various systems which utilize depression to ensure functions related to the operation of the heat engine or to the driving and to the safety of the vehicle: variable-geometry turbocharger, exhaust gas recirculation system (EGR), assisted brake pressure amplifier, etc. The depression is also utilized to ensure some depollution functions, such as the purging of the vapors absorbers on gasoline-fuelled vehicles, or the recycling of the crankcase gases.
For vacuum piloting or assisting functions, the depression is created by the intake in the case of an atmospheric gasoline engine, or by a vacuum pump driven by the camshaft of a diesel engine or a turbocharged gasoline engine, or still by an electric pump, and this depression is maintained by a check valve.
In the case of brake assistance, a vacuum check valve is installed to guarantee that the vacuum is preserved in all circumstances, including the case of switch off of the vacuum generation source, in particular in case of shutdown of the vehicle engine, in order to preserve the brake assistance. Well maintaining the depression thus constitutes a security requirement and a lot of efforts are made to guarantee a depression maintenance time as long as possible, after shutdown of the engine, and to reduce the vacuum (re)establishing time in the brake assistance circuit.
In the case of the management of flows of gasoline vapors and/or oil vapors, particularly for depollution functions, the vapors must be injected in the engine air intake in order to be burnt in the latter. For a turbocharged engine, depending on the turbocharger speed, these vapors are injected upstream or downstream of the turbocharger. In addition, pressurizing the turbocharger should not affect the operation of the vapors recycling system. Thus, it is essential to equip the circuits of this system with one or more check valve(s), to control the gaseous flows. For example, in an oil vapor recycling system, two check valves are provided, with one first check valve inserted on a vapor injection duct upstream of the turbocharger, and one second check valve inserted on a vapor injection duct in the air intake, downstream of the turbocharger, this last valve having to resist the turbocharger pressure.
The check valves currently utilized in this kind of applications include various closing means. Among these, the valves with plastic bodies, utilizing as a closing means a flexible rubber membrane, constitute the majority of current achievements. As an example of a check valve with membrane, reference is made to patent document EP 1 314 920 A2, in which the membrane is maintained by its periphery in the body of the valve.
There are also known achievements of check valves with membrane, in which the membrane, pierced in its center, is fastened on a central pin which is itself carried by the seat of the valve, the periphery of the membrane being free in that case—see patent document CN 201705473 U.
In such a check valve, in the closing position, sealing is ensured by:                a surface contact between the periphery of the membrane and the circular outer edge protruding from the seat,        a surface contact of the membrane with one face of the seat,        and also, in the case of a membrane assembled on a central pin, an interference between the edge of the central hole of the membrane and the periphery of the pin.        
The contact at rest, that is to say in the absence of differential pressure, between the membrane and the seat, is obtained by a permanent elastic deformation of the membrane, itself resulting both from the conforming of the body and of the seat of the valve and from the positioning of the membrane itself.
The requirements usually imposed on this kind of check valves consist in having a valve with very low opening pressure and pressure drops in the passing direction of the fluid, and also in having a good pressure resistance in the direction opposite to the flow.
These requirements are contradictory, because they impose to have, on the one hand, a very flexible membrane and great passage sections for the fluid, and in the other hand, little ports and a relatively rigid membrane.
Usually, the passage of the fluid inside the valve, in the passing position, is achieved by circular ports arranged in the seat under the membrane. These circular ports are particularly arranged all around the central pin on which the membrane is maintained.
The current circular shape of the ports exhibits important drawbacks.
First, the circular shape of the ports is not optimal from the point of view of the available flowing section for the gaseous flow. Thus, it causes high pressure drops, which is penalizing in the applications where it is desirable to have a maximum flow rate, for example to optimize a depollution function.
Furthermore, in the case of vacuum piloting or assisting functions, it is necessary to be capable of establishing the vacuum as quickly as possible, so as to have the energy source constituted by this vacuum as soon as possible. A limited passage section and high pressure drops do not allow obtaining, for the valve, good performances in terms of vacuum establishing time for this kind of applications.
Moreover, the circular ports have a sharp-ridged edge, without rounding. Thus, in the case where the membrane must resist a certain pressure in the non-passing direction of the valve, for example during the turbocharger startup, the absence of rounding causes an important local stress on the membrane, with risks of crackings or even tearings of this membrane.